In plate type heat exchangers, fluids exchange heat whilst flowing through heat exchange zones between adjacent (stacked) peripherally sealed thin metal plates. These heat exchangers offer the attractions of true counter-current thermal contact, a large easily adjustable surface area-to-volume ratio, compactness and sparing use of expensive materials. Plate type heat exchangers are the most popular alternative to the more conventional shell-and-tube type heat exchangers for these reasons.
The most common plate type heat exchanger is the gasketed plate style in which the fluid delivery and return ports and the plate peripheries are sealed with a gasket. The thin metal plates are pressed to form the gasket locations, fluid distribution zones and corrugations which enhance heat transfer and which provide mechanical strength in the heat exchange zone. The plate stack is held together with heavy end plates which are mechanically supported by tie rods or a press. This style of heat exchanger offers the advantage of easy disassembly for cleaning, but it suffers from the drawbacks that the gaskets tend to limit the range of fluids and temperatures which can be handled, pressure containment is somewhat limited and a limited number of stock pressed metal plate designs must serve all duties. The desirability of eliminating elastomeric gaskets in some circumstances has led to the welded plate, spiral and lamella styles. However, these cannot be completely disassembled.
In the cyrogenics field a brazed aluminium plate-fin style of exchanger has been developed. Corrugated aluminium sheets (fins) and sealing bars are brazed to the flat plates which separate the fluids, with the delivery and return ports being attached to the plate edges where gaps are left in the sealing bars. This construction technique relies on brazing to provide thermal and mechanical bonds and so is limited to materials which can suitably be brazed and to the use of fluids and temperatures which are compatible with them.
The plate type heat exchanger to which the present invention relates differs from those mentioned above in the manner of plate production and assembly, and it offers the promise of cost savings in some applications. In the above described (prior art) heat exchangers, the fluid flow passages are formed by spacing apart the flat or pressed metal plates with gaskets or metal sealing bars. In the heat exchanger to which the present invention relates, the fluid flow passages are formed within the thickness of substantially flat plates. A heat exchanger having plates of the type to which the present invention relates is disclosed in Australian Patent Application No. 70211/81, filed May 4, 1981 in the name of University of Sydney.
In all plate type heat exchangers, provision should be made for even distribution of fluid across the full width of the heat exchange zone, since any tendency of fluids to adopt an uneven flow can be detrimental to performance. Some sort of distribution zone is generally required to connect a fluid inlet port to the heat exchange zone. This is because, due to practical requirements, the length of a port edge available to deliver fluid to the heat exchange zone is generally shorter than the width of the heat exchange zone itself and/or because the port edge is not wholely perpendicular to the direction of flow in the heat exchange zone. In each case the effective transverse extent of the port is less than the width of the heat exchange zone.
The above referenced patent application discloses heat exchange plates having a distribution zone in the form of a single channel which, through branch channels, connects the inlet and outlet ports of the device to a heat exchange zone.